1. Field of the Invention
The present invention relates to variable power optical systems having a vibration control function and image pick-up apparatuses using the system, and in particular relates to an image pick-up apparatus, such as a video camera, a camera for silver halide photography, an electronic still-camera, and a digital camera, and a variable power optical system having a vibration control function suitably used for the apparatus, wherein when the variable power optical system is vibrated (tilted), image blurring is optically corrected by shifting a part of lens groups of the variable power optical system in a direction orthogonal to the optical axis so as to obtain still images.
2. Description of the Related Art
When a picture is taken from a running mobile unit, such as a vehicle and an aircraft, vibration is transmitted to a photo-shooting system to cause camera shake, thereby generating image blurring.
Hitherto, various vibration control optical systems having the function of preventing image blurring have been proposed.
For example, in Japanese Patent Laid-Open No. 56-21133, image stability is promoted by shifting a part of optical members in a direction for canceling image vibratory displacement due to vibration in accordance with an output signal from detecting means for detecting vibrating conditions in an optical apparatus. In Japanese Patent Laid-Open No. 61-223819, in an image pick-up system in which a prism having a variable apex angle is placed in the closest position to an object, image stability is promoted by changing the apex angle of the prism having the variable apex angle.
In Japanese Patent Laid-Open No. 1-116619 and Japanese Patent Laid-Open No. 2-124521, a still image is obtained by vibrating a part of lens groups in an image pick-up system in a direction orthogonal to the optical axis in accordance with a signal obtained by detecting the vibration of the image pick-up system by utilizing an acceleration sensor, etc.
In Japanese Patent Laid-Open No. 7-128619, a variable power optical system comprises four lens-groups of, in order from an object, a first group having a positive refracting power that is fixed during a variation in magnification and in-focusing, a second group having a negative refracting power having a magnification varying function, an iris, a third group having a positive refracting power, and a fourth group having a positive refracting power having a function of correcting changes in an image plane due to the variable power and in-focussing function as well, wherein the third group comprises two lens-groups of a thirty-first group having a negative refracting power and a thirty-second group having a positive refracting power, and the image blurring produced when the variable power optical system is vibrated is corrected by shifting the thirty-second group in a direction orthogonal to the optical axis.
In Japanese Patent Laid-Open No. 7-199124, a variable power optical system formed of four lens-groups having a positive, a negative, a positive, and a positive refracting power, respectively, controls vibration by vibrating the entire third group.
On the other hand, Japanese Patent Laid-Open No. 10-62687 proposes a zoom lens formed of four lens-groups respectively having a positive, a negative, a positive, and a positive refracting power, wherein high performance is achieved while the entire length of the lens is reduced by a variation in magnification the second and the third lens-group and by forming the first lens-group of positive singlet lenses.
In general, in a method for obtaining still images wherein image blurring is eliminated by placing a vibration control optical system in front of an image pick-up system and by vibrating a part of operating lens-groups in the vibration control optical system, there has been the problem that the entire size of the apparatus is increased and the shifting mechanism of the operating lens-groups is complicated.
In a vibration control optical system utilizing a prism having a variable apex angle, there has been the problem that chromatic aberration having a decentering magnification is increased during vibration control when the focal length is large, in particular.
On the other hand, in an optical system wherein vibration control is performed by decentering in parallel a part of operating lens-groups of an image pick-up system in a direction orthogonal to the optical axis, there has been the problem that a space for shifting lenses is needed and decentering aberration during vibration control is increased, even through there is the advantage of not requiring an additional optical system for vibration control.
In a variable power optical system formed of four lens-groups respectively having a positive, a negative, a positive, and a positive refracting power, when vibration control is performed by shifting the entire third lens-group in a direction orthogonal to the optical axis, there has been the problem that when the third lens-group is formed to be of a telephoto type having a positive lens and a negative meniscus lens so as to reduce the entire length, decentering aberration such as decentering coma or the decentering distortion on an image plane is produced therein, thereby causing the image quality to deteriorate.
Furthermore, in the conventional zoom lenses described above, although the zoom lens having a zooming ratio of eight or more is matched to a video camera, etc., it is insufficient in view of correcting aberration for use as an electronic still camera having an image pick-up element equivalent to one million pixels.
Accordingly, it is an object of the present invention to provide a variable power optical system and an image pick-up apparatus using the system wherein the image blurring produced when the variable power optical system is vibrated (tilted) is corrected by shifting a comparatively small-sized and lightweight lens group forming a part of the variable power optical system in a direction orthogonal to the optical axis, and wherein the system has a vibration control function having properly corrected decentering aberration produced when the lens group is decentered and sufficiently matching to an electronic still camera having one million pixels or more, for example, while a miniaturized apparatus and a simplified mechanism are obtained by properly forming the lens group for correcting the blurring.
To this end, in accordance with a first aspect, the present invention relates to a variable power optical system comprising, in order from an object side a first lens group having a positive refracting power and consisting of a positive singlet lens or the combination of one positive lens and one negative lens, a second lens group having a negative refracting power, a third lens group having a positive refracting power, and a fourth lens group having a positive refracting power. At least the second lens group and the third lens group are moved during a variation in magnification, and an image is displaced by shifting any one of the entire second lens group and the entire third lens group so as to have a component in a direction orthogonal to an optical axis of the optical system.
Preferably, when the image is displaced by shifting the entire third lens group so as to have a component in the direction orthogonal to the optical axis, the optical system satisfies the condition (1) discussed below. Further, when the image is displaced by shifting the entire second lens group so as to have a component in a direction orthogonal to the optical axis, the optical system satisfies the conditions (2) and (3) discussed below. Moreover, when the image is displaced by shifting the entire second lens group so as to have a component in a direction orthogonal to the optical axis, the optical system satisfies the condition (4) discussed below.
The third lens group preferably comprises a plurality of positive lenses and one negative lens having a concave surface facing the image side. More specifically, the third lens group may preferably consist of, in order from the object side, a positive lens, bonded lenses comprising a positive lens and one negative lens having a concave surface facing the image side, and a positive lens. Further, the positive lens disposed closest to the object side in the third lens group is an aspherical lens. In addition, the second lens group preferably consists of, in order from the object side, a negative meniscus lens having a concave surface facing the image side, a negative lens, and a positive lens having a convex surface facing the object side. Also, the first lens group consists of a positive singlet lens and satisfies the conditions (5) and (6) discussed below.
According to yet another aspect, the present invention that achieves at least one of these objectives relates a variable power optical system comprising, in order from an object side a first lens group having a positive refracting power, a second lens group having a negative refracting power, a third lens group having a positive refracting power, and a fourth lens group having a positive refracting power. The first lens group, the second lens group, and the third lens group are moved during a variation in magnification, and an image is displaced by shifting the entire third lens group so as to have a component in a direction orthogonal to an optical axis of the variable power optical system.
The optical system preferably satisfies the condition (7) discussed below. In addition, the second lens group preferably consists of, in order from the object side, a negative meniscus lens having a concave surface facing the image side, a negative lens, and a positive lens having a convex surface facing the object side.
According to another aspect, the present invention that achieves at least one of these objectives relates to an image pick-up apparatus comprising a variable power optical system, a casing for holding the variable power optical system, and an image pickup element supported by the casing and positioned to receive light from the variable power optical system. The optical system comprises, in order from an object side a first lens group having a positive refracting power and consisting of a positive singlet lens or the combination of one positive lens and one negative lens, a second lens group having a negative refracting power, a third lens group having a positive refracting power, and a fourth lens group having a positive refracting power. At least the second lens group and the third lens group are moved during a variation in magnification, and an image is displaced by shifting any one of the entire second lens group and the entire third lens group so as to have a component in a direction orthogonal to an optical axis of the optical system.
According to another aspect, the present invention that achieves at least one of these objectives relates to an image pick-up apparatus comprising a variable power optical system, a casing for holding the variable power optical system, and an image pickup element supported by the casing and positioned to receive light from the variable power optical system. The optical system comprises, in order from an object side a first lens group having a positive refracting power, a second lens group having a negative refracting power, a third lens group having a positive refracting power, and a fourth lens group having a positive refracting power. The first lens group, the second lens group, and the third lens group are moved during a variation in magnification, and an image is displaced by shifting the entire third lens group so as to have a component in a direction orthogonal to an optical axis of the variable power optical system.
According to another aspect, the present invention that achieves at least one of these objectives relates to a method of compensating for image blurring that occurs when a variable power optical system is tilted. The variable power optical system comprises a first lens group having a positive refracting power and consisting of a positive singlet lens or the combination of one positive lens and one negative lens, a second lens group having a negative refracting power, a third lens group having a positive refracting power, and a fourth lens group having a positive refracting power. The method comprises the steps of moving at least the second lens group and the third lens group during a variation in magnification and displacing an image by shifting any one of the entire second lens group and the entire third lens group so as to have a component in a direction orthogonal to an optical axis of the variable power optical system.
The shifting step preferably comprises the step of satisfying condition (1) when the image is displaced by shifting the entire third lens group so as to have a component in the direction orthogonal to the optical axis, wherein the magnification at a telephoto end of the third lens group is B3t and the magnification at the telephoto end of a lens group disposed toward the image from the third lens group is Brt.
The shifting step can also comprise the step of satisfying conditions (2) and (3) when the image is displaced by shifting the entire second lens group so as to have a component in a direction orthogonal to the optical axis. Moreover, the shifting step can comprise the step of satisfying condition (4) when the image is displaced by shifting the entire second lens group so as to have a component in a direction orthogonal to the optical axis, wherein the magnification at a telephoto end of the second lens group is B2t and the magnification at the telephoto end of a lens group disposed toward the image from the second lens group is Brt.
The third lens group preferably comprises a plurality of positive lenses and one negative lens having a concave surface facing the image side, and more specifically consists of, in order from the object side, a positive lens, bonded lenses comprising a positive lens and one negative lens having a concave surface facing the image side, and a positive lens. In addition, the positive lens disposed closest to the object side in the third lens group is an aspherical lens. Further, the second lens group preferably consists of, in order from the object side, a negative meniscus lens having a concave surface facing the image side, a negative lens, and a positive lens having a convex surface facing the object side. Also, the first lens group consists of a positive singlet lens and satisfies conditions (5) and (6).
According to another aspect, the present invention that achieves at least one of these objectives relates to a method of compensating for image blurring that occurs when a variable power optical system is tilted. The variable power optical system comprises, in order from the object side, a first lens group having a positive refracting power, a second lens group having a negative refracting power, a third lens group having a positive refracting power, and a fourth lens group having a positive refracting power. The method comprises the steps of moving the first lens group, the second lens group, and the third lens group during a variation in magnification, and displacing an image by shifting the entire third lens group so as to have a component in a direction orthogonal to an optical axis of the variable power optical system. The optical system preferably satisfies condition (7). And, the second lens group preferably consists of, in order from the object side, a negative meniscus lens having a concave surface facing the image side, a negative lens, and a positive lens having a convex surface facing the object side.